Abstract
This study investigated the diel emission of volatile organic compounds (VOCs) from intact apple (Malus
x domestica Borkh., cv. Golden Delicious) and grape (Vitis vinifera L., cv. Pinot Noir) foliage. Volatiles were monitored continuously for 48 h by proton transfer reaction - time of flight - mass spectrometry (PTRToF-MS). In addition, volatiles were collected by closed-loop-stripping-analysis (CLSA) and characterized by gas chromatography-mass spectrometry (GC-MS) after 1 h and again 24 and 48 h later. Fourteen and ten volatiles were characterized by GC-MS in apple and grape, respectively. The majority of these were terpenes, followed by green leaf volatiles, and aromatic compounds. The PTR-ToF-MS identified 10 additional compounds and established their diel emission rhythms. The most abundant volatiles displaying a diel rhythm included methanol and dimethyl sulfide in both plants, acetone in grape, and mono-, homo- and sesquiterpenes in apple. The majority of volatiles were released from both plants
during the photophase; whereas methanol, CO2, methyl-butenol and benzeneacetaldehyde were
released at significantly higher levels during the scotophase. Acetaldehyde, ethanol, and some green leaf
volatiles showed distinct emission bursts in both plants following the daily light switch-off. These new
results obtained with a combined analytical approach broaden our understanding of the rhythms of
constitutive volatile release from two important horticultural crops. In particular, diel emission of sulfur
and nitrogen-containing volatiles are reported here for the first time in these two crops.